Method for adapting link weights in ralation to optimized traffic distribution

ABSTRACT

The invention relates to a method which is used to adapt link weights or, link costs, for optimized traffic distribution within a communication network. According to said method, a loop is circulated until an interruption criterion is met. The individual iterations comprise the following steps: Routing of traffic within the communication network is calculated based on link cost paths. Parameter values used for optimization e.g. the link-related volume of traffic, are determined for the individual links by means of the calculated path, and an expected volume of traffic and the link are determined for the parameter having the highest value. When the highest determined value is equal to or less than the valve of the previous step (interruption criterion), the link costs are increased for the determined link. Said method enables link costs and paths for optimized traffic distribution to be determined in an economical manner.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2005/050149, filed Jan. 14, 2005 and claims the benefitsthereof. The International Application claims the benefits of Germanapplication No. 10 2004 004 793.6 filed Jan. 30, 2004, both applicationsare incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The invention relates to a method for adapting link weights in acommunication network formed from links for an optimized distribution oftraffic within the communication network as regards the volume oftraffic expected for the communication network and in relation to aparameter relating to link usage.

SUMMARY OF THE INVENTION

The invention lies within the area of communication technology and inparticular deals with the transmission of data over packet-orientednetworks.

The optimization of data transmission over packet-oriented networks,especially over IP (Internet Protocol)-based networks is currently animportant area of activity in the field of network technologies. thetransmission of data with different quality-of-service requirements inparticular being a prerequisite for the provision of new services, suchas for example the transmission of real-time traffic overpacket-oriented networks. To optimize transmission as much as possible,different parameters, such as delay, noise susceptibility or trafficdistribution must be taken into account.

The best possible distribution of the traffic routed over acommunication network is important, on the one hand in relation toavoiding overload situations, on the other hand good trafficdistribution is the requirement for a good utilization of the existingresources and especially the bandwidth available. The trafficdistribution within a communication network depends on the routingwithin the network or the paths on which the traffic is routed throughthe network. By far the most widespread routing method forpacket-oriented networks based on an IP protocol is what is known as theOSPF (Open Shortest Path First) method or protocol. In this method, fortraffic to be routed between two nodes, the shortest path in the senseof a metric between the two nodes is defined. The path is normallydetermined with the aid of what are known as link costs. The terms linkweight or link weights which are normally employed by specialists assynonymous with link costs are also referred to below. The link costs orlink weights are values administratively assigned to the links, saidvalues representing a measure of how well the relevant link is beingused. In the simplest case the link costs are equal to 1 for each link,i.e. all links are treated in the same way. For routing which minimizesthe link costs this method automatically determines the shortest pathbetween two nodes as regards the number of links or the number of hops.Changing the link costs allows the determination of the routes and thusthe distribution of the traffic within a communication network to beinfluenced. Controlling the traffic distribution by adapting the linkcosts is generally possible with routing methods which operate using ametric and the allocation of link costs, e.g. in the IS-IS (IntermediateSystem-Intermediate System) protocol or for example the ECMP (Equal CostMultiple) method, which was defined within the framework of the OSPFprotocol and makes provision for the use of a number of paths determinedby means of OSPF for routing between two nodes.

Conventional methods for optimizing traffic distribution by adapting thelink costs are comparatively complicated. Usually the link costs areoptimized globally by optimizing a target function which reflects thetopology of the network. Because of the complexity of this method thelink costs are currently frequently not optimized. Unavoidableadaptations of the link costs are frequently performed manually, whichentails a high risk of errors. Thus the traffic optimization in realnetworks is likely to be less than optimal.

The object of the invention is to specify a simple method fordetermining the link costs in a communication network as regardsoptimized traffic distribution

The object is achieved by the claims.

The thinking behind the invention is that the link costs or link weightsof heavily loaded links should be increased to reduce the traffic loadon these links. A parameter is used for the optimization whichrepresents the measure of the loading of the individual links.Preferably this parameter is specified by the traffic load of theindividual links. Other options are the relative traffic load inrelation to the link bandwidth, any traffic-dependent costs arising forlink usage (possibly even in the form of real charges arising), theavailability of the links, the run time on the individual links or theload-bearing capabilities of the end nodes of the links concerned. Thestarting point of the invention is that the volume of traffic to becarried by the network is known or at least an estimate of said volumeexists. In traffic theory what is known as the traffic matrix is usuallyused to specify the traffic volume more precisely. The traffic matrixspecifies the volume of traffic to be transported between pairs ofsource and destination nodes. For traffic routed through thecommunication network a source node for example corresponds to aningress node and a destination node to an egress node, so that thetraffic matrix features an entry in relation to these two nodes for thetraffic transported between them.

For optimization as regards the parameter the procedure is as follows.First the link costs of the individual links are initialized, i.e. startvalues are assigned to them. For the links a distinction is preferablymade between the two directions, i.e. a connection between two nodescorresponds to two directed links, each of which transports the trafficonce from the first node to the second and once in the other direction.The invention can then be further developed so that, especially forsymmetrical traffic matrices, the optimization of the link costs isperformed for both directions simultaneously. After the assignment ofstart values for the link costs paths for the routing of traffic withina communication network are computed with the aid of the routingprotocol (for example OSPF or IS-IS). With the aid of the assumedtraffic volume the traffic carried on these paths and thereby thetraffic volume on the individual links can be calculated or determined.The link is then determined for which the parameter, for example thetraffic volume, has the highest value. Subsequently the value of thelink costs for the link determined is increased, by 1 for example.Calculating the paths, defining the values of the parameter, determiningthe link for which the parameter has the highest value and increasingthe value of the link costs for the link determined is performed as aloop which is run until such time as the value of the parameter for thelink with the highest parameter value determined in a step is higherthan the parameter determined in the previous step or sequence for thelink with the highest parameter value. If this abort criteria isfulfilled, the values for the link costs defined in the step before lastand the associated paths for routing within the communication networkare determined.

An improved or optimized traffic distribution is obtained through theinvention by increasing the link costs of heavily loaded links. Incomparison to conventional methods the inventive method is simpler andcan be implemented without any problems. For determining paths withinthe framework of the ECMP (Equal Cost Multiple) method it is useful tooperate in the method with whole-number link costs or whole-numberincreases in the link costs, since in this way it is more likely thatalternative paths with the same accumulated costs for the connection oftwo nodes are produced, so that, as provided for in the ECMP method,traffic can be distributed to the various equivalent paths. As a startpoint it is useful to initialize all link costs with the same value, forexample with 1.

The inventive method can be performed using central or distributedcomputing capacity. For parts thereof, e.g. path calculation, there canbe recourse to conventional methods (which for example are definedwithin the framework of the OPSF or IS-IS protocol).

The object of the invention is explained in more detail below within thecontext of an exemplary embodiment which refers to a flowchart.

BRIEF DESCRIPTION OF THE DRAWING

The sole FIGURE shows an exemplary flowchart according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The exemplary embodiment starts from the assumption that thecommunication network is an IP network which is formed with nodes andlinks and that paths are to be determined for routing within theframework of the ECMP concept. To begin with the link costs LK areinitialized with the value 1. On the basis of these link costs LK theECMP paths P(LK) are then calculated. The calculation is undertaken bydetermining the paths with the lowest accumulated link costs LK forrouting between two nodes, as is provided for in the OSPF protocol.

Least-cost paths to a destination node can for example be determined inthe following way. All neighboring nodes of the destination node areinitially determined and these neighboring nodes are assigned the linkcosts as node costs. This defines the routing for this first ring ofnodes around the destination node. The procedure below is undertakenring-by-ring, moving up from a ring to the next higher ring in eachcase. A ring in this case is specified by the fact that a specificnumber of links at least have to be passed through to reach thedestination node. The costs of the individual paths are successivelycalculated ring-by-ring. In this case in each step the path costs aremade up of the sum of the link costs and the node costs, with link costsbeing the current costs of the outgoing link in each case and the nodecosts being the actual costs of the relevant end node of this link ineach case. The costs of the paths calculated in this way are thencompared and only those paths are retained which have minimal path costs(as is also provided for within the framework of the OSPF concept). Anumber of paths with the minimum path costs are frequently found whichare retained for traffic distribution in the sense of the ECMP concept.Other methods of determining least-cost paths, for example the Dijkstraalgorithm, can be used just as well.

The above procedure can be used for re-determining the paths as part ofthe iterations for which the inventive method makes provision. Aftercalculation of the paths P(LK) as a function of the link costs, thetraffic matrix VM is used to determine the traffic volume V(L) of theindividual links. The link L(Vmax,n) with the highest or maximum trafficvolume Vmax,n is identified and the maximum traffic volume Vmax,n inthis step is compared with the maximum traffic volume Vmax,n−1 in theprevious step If the maximum traffic volume Vmax,n for the current stepis less than the maximum traffic volume Vmax,n−1 for the previous step,the link costs LK(L(Vmax,n)) of the link L(Vmax,n) with the maximumtraffic volume Vmax,n are increased by 1 and the paths P(LK) arerecalculated as a function of the changed link costs LK. The loop isthen executed once more. Otherwise, i.e. if the maximum traffic loadVmax,n is greater than in the previous step, the link costs LKdetermined in the previous step are used as optimized link costs LKOptand the associated paths P(LK) are used as the paths P(LKopt) determinedfor an optimized traffic distribution for routing.

1.-8. (canceled)
 9. A method for adapting link weights in acommunication network formed with links for an optimized trafficdistribution within the communication network in respect of a trafficvolume expected for the communication network and in relation to aparameter relating to the link usage, the method comprising: a)assigning start values for the link weights to the links of thecommunication network; b) calculating paths for routing of trafficwithin the communication network on the basis of the link weights; c)determining the values of the parameter for the links using thecalculated paths and the expected traffic volume; d) determining suchlink for which the parameter has the highest value; and e) increasingthe link weight for the determined link, wherein f) the steps b), c), d)and e) are repeated until the value of the parameter for the determinedlink is higher than the parameter value for the determined link relativeto a preceding step d), wherein the steps a) to f) are performed withthe aid of a data processor.
 10. The method in accordance with claim 9,wherein the parameter is produced by an absolute traffic load, arelative traffic load related to link bandwidth traffic-related costsarising for using the link, a link availability, a delay time of therelevant link, or the load capabilities of an end node of the relevantlink.
 11. The method in accordance with claim 9, wherein the startvalues for the link weights are the same for all links.
 12. The methodin accordance with claim 10, wherein the start values for the linkweights are the same for all links.
 13. The method in accordance withclaim 9, wherein the paths are calculated using the OSPF (open shortestpath first) protocol or the IS-IS (Intermediate System-IntermediateSystem) protocol.
 14. The method in accordance with claim 10, whereinthe paths are calculated using the OSPF (open shortest path first)protocol or the IS-IS (Intermediate System-Intermediate System)protocol.
 15. The method in accordance with claim 11, wherein the pathsare calculated using the OSPF (open shortest path first) protocol or theIS-IS (Intermediate System-Intermediate System) protocol.
 16. The methodin accordance with claim 9, wherein the paths calculated if the abortcriterion f) is fulfilled are used for routing within the framework ofthe ECMP (Equal Cost Multi Path) concept.
 17. The method in accordancewith claim 10, wherein the paths calculated if the abort criterion f) isfulfilled are used for routing within the framework of the ECMP (EqualCost Multi Path) concept.
 18. The method in accordance with claim 11,wherein the paths calculated if the abort criterion f) is fulfilled areused for routing within the framework of the ECMP (Equal Cost MultiPath) concept.
 19. The method in accordance with claim 13, wherein thepaths calculated if the abort criterion f) is fulfilled are used forrouting within the framework of the ECMP (Equal Cost Multi Path)concept.
 20. The method in accordance with claim 9, wherein the linkweights and their increase are always expressed by whole numbers. 21.The method in accordance with claim 10, wherein the link weights andtheir increase are always expressed by whole numbers.
 22. The method inaccordance with claim 11, wherein the link weights and their increaseare always expressed by whole numbers.
 23. The method in accordance withclaim 9, wherein the link weight is increased for both directions oftransmission of the link for the link determined.
 24. The method inaccordance with claim 10, wherein the link weight is increased for bothdirections of transmission of the link for the link determined.
 25. Themethod in accordance with claim 11, wherein the link weight is increasedfor both directions of transmission of the link for the link determined.26. The method in accordance with claim 9, wherein the expected trafficvolume is described by the traffic matrix.
 27. The method in accordancewith claim 10, wherein the expected traffic volume is described by thetraffic matrix.